BANGALORE, Oct 12 (Reuters) - Shares of Digital River Inc DRIV.O slumped 41 percent, after the e-commerce services provider said its top customer Symantec (SYMC.O) will not extend an existing contract to manage its online traffic.

On a conference call with analysts, the company also said it may not provide an outlook for 2010 when it reports its quarterly results on Nov. 3

The news triggered the stock's biggest single-day fall in seven years, trimming the company's market capitalization to about $973.9 million from about $1.56 billion.

Digital River's products and services have helped drive traffic to Symantec's North American e-commerce sites and launch managed paid search and e-mail programs.

Digital River said Symantec expects to move all the online traffic currently outsourced to Digital River to an internally developed e-commerce system before the current contract expires on June 30, 2010.

"Symantec's decision to take it in-house came as a big surprise to us," JMP Securities analyst Sameet Sinha said.

In 2008, sales of products to Symantec accounted for about 24 percent of Digital River's revenue, while sales from proprietary Digital River services to Symantec consumers accounted for 9 percent of revenue.

Symantec contributed about 32 percent to both revenue and earnings before interest, taxes, depreciation and amortization, Sinha said. "So it's going to have significant impact."

EBITDA could be down 25 percent in 2010, assuming that the entire Symantec business goes away in the beginning of 2010, Sinha said.

Lazard Capital Markets downgraded Digital River to "hold" from "buy," following the news.

"We estimate that earnings per share on an annualized basis would decline by about $0.75 without Symantec, assuming a corresponding reduction in headcount, along with lower infrastructure, service and platform expenses," analyst Colin Sebastian said in a note to clients.

Digital River said it expects third-quarter results to be at or slightly above the top end of its outlook.

In July, the company forecast third-quarter earnings of 38 cents to 41 cents a share, excluding items, on revenue of $96.5 million to $98.5 million.

Digital River estimates sequential revenue from its non-Symantec business to have grown at about 8 percent in the third quarter, compared with about 2 percent growth in the second quarter.

On the call, the company said it would provide a non-Symantec revenue outlook on Nov. 3.

Shares of Digital River fell to a low of $23.82, before paring some losses to trade at $24.95 Monday on Nasdaq. (Editing by Himani Sarkar, Deepak Kannan Anil D'Silva)